Analysis of the Effect of Drainage Management on Drainage Water Salinity in Rice-canola Cropping Rotation

While providing conditions for crop diversification and improving productivity of northern Iran’s paddy fields¡ subsurface drainage can be a threat to downstream water resources. This research was done to quantify the effects of two types of conventional water management in rice cultivation systems including midseason drainage and alternate irrigation and drainage as well as free drainage in canola growing season on salinity of subsurface drainage effluents. Required experiments were conducted on subsurface drained paddy fields during 4 rice growing seasons and two canola growing seasons (2011- 2015). Each type of management strategy was repeated twice during the study period. Measurements of water table depth and drain discharge were done during drainage periods of different growing seasons. Moreover¡ drainage water salinity was measured in due times. Alternate drainage and increase in water table depth raised drainage water salinity in rice and canola seasons¡ respectively. Compared with midseason drainage¡ alternate irrigation and drainage resulted in 121- 420 kg ha-1 increase in salt loss in different drainage systems. Salt discharge was considerably higher in canola season than rice season due to free drainage condition in canola seasons. Total salt load under midseason drainage¡ alternate irrigation and drainage and canola cropping through different drainage systems ranged¡ respectively¡ 78.4-365¡ 240- 695 and 3056- 5656 kg ha-1. Based on the results¡ water table management through installation of shallow- suitable spaced drains can be effective to decrease salt load from subsurface drained paddy fields.